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  1. #14
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,512
    if they did not remove the piston what else did they do wrong .tell the company to send out a different tech to remove the piston . the airflow setting on that system is very important blower is probably on high and will need adjusted

  2. #15
    Join Date
    Jul 2008
    Location
    Coastal North Carolina
    Posts
    10
    When a txv is udes before a piston, the piston does restrict the refrigerant flow. A piston is designed to meter refrigerant based on the liquid line pressure. If your pressure is 225, then the predrilled hole will reduce the pressure from that point. When a txv is installed, it will reduce the pressure within the valve, so the original orfice will only experience a pressure of about 90, due to the high superheat, and the txv throttled completely open. There is a hugh difference between the operating suction pressure of a piston being fed at 90 psig, and 200 psig. Then you actually have to take into account that the txv/piston combination isnt getting a solid stream of liquid to the piston, thus dropping the pressure further.

    In my experience, if a piston has been left in, with a txv installed, the suction pressure will be low, the discharge will be high, and the superheat will be high and the subcooling will be high. There is no need to eyeball this, being that a subcooling and superheat check will tell you if the evaporator is performing correctly. No need to lay eyes on the device when the tests will tell you all you need to know.

  3. #16
    Join Date
    Nov 2001
    Location
    east kansas
    Posts
    8,012
    If it's a current Goodman coil and a TX_ _ _ kit with a Parker TXV I doubt they left the piston in. On those TXVs there is a little tit that is manufactured on the outlet of the TXV. I've been told that tit is to idiot proof the TXV installation. You can't leave the piston in and still install the TXV. It won’t fit. So I've been told.

    I of course have never tried to install a TXV without taking out the piston.
    Beware of advice given by some guy on the Internet.

  4. #17
    Join Date
    Apr 2007
    Posts
    623
    [QUOTE=Milk man;1939563]in. On those TXVs there is a little tit that is manufactured on the outlet of the TXV.


    Is that at technical term. I know technology is advancing but if they start putting t**s on them , they will be even easier to sell!

  5. #18
    Join Date
    Nov 2001
    Location
    east kansas
    Posts
    8,012
    I just like using terms such as tit and nipple. My wife, just aftewr we got married, thought I was just being a typical male when I told her to hand me a nipple out of my nipple tray.
    Beware of advice given by some guy on the Internet.

  6. #19
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,852
    Quote Originally Posted by beenthere View Post
    Maybe Robo will put a Piston in his this weekend yet, and tell you how much of a difference it makes.

    Have yours removed.
    I already have a piston.

    I'll need to install a txv and replace the piston with a larger sized one.

    Seeing that I still have not got around to finishing my condensate pump drain and am still using a bucket with a cut off switch, how soon do you think I will get to doing this experiment?
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  7. #20
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,852
    Quote Originally Posted by PDQuick View Post
    When a txv is udes before a piston, the piston does restrict the refrigerant flow. A piston is designed to meter refrigerant based on the liquid line pressure. If your pressure is 225, then the predrilled hole will reduce the pressure from that point. When a txv is installed, it will reduce the pressure within the valve, so the original orfice will only experience a pressure of about 90, due to the high superheat, and the txv throttled completely open. There is a hugh difference between the operating suction pressure of a piston being fed at 90 psig, and 200 psig. Then you actually have to take into account that the txv/piston combination isnt getting a solid stream of liquid to the piston, thus dropping the pressure further.

    In my experience, if a piston has been left in, with a txv installed, the suction pressure will be low, the discharge will be high, and the superheat will be high and the subcooling will be high. There is no need to eyeball this, being that a subcooling and superheat check will tell you if the evaporator is performing correctly. No need to lay eyes on the device when the tests will tell you all you need to know.
    Good points. This thread has really brought out the technical geek in me

    Oh, I do agree that the OPs system should not be being used as an experiment and that the piston needs to be removed. What I'd like to know is how it is known that the piston is still in there?
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  8. #21
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,852
    Quote Originally Posted by Milk man View Post
    I just like using terms such as tit and nipple. My wife, just aftewr we got married, thought I was just being a typical male when I told her to hand me a nipple out of my nipple tray.
    Your username is starting to make more sense now
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  9. #22
    Join Date
    Jul 2008
    Location
    Coastal North Carolina
    Posts
    10
    Quote Originally Posted by RoBoTeq View Post
    What I'd like to know is how it is known that the piston is still in there?

    Well, if it is in there, and is affecting the system negatively, you would have high superheat and subcooling. If it isnt affecting these things, and you still want to know, a 5/16th nutdriver, 2 wrenches, and a flashlight need to be in your hand!

  10. #23
    Join Date
    Nov 2001
    Location
    east kansas
    Posts
    8,012
    Quote Originally Posted by RoBoTeq View Post
    Your username is starting to make more sense now
    You know, just when you piss me off you say something like that.
    Beware of advice given by some guy on the Internet.

  11. #24
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,804
    Quote Originally Posted by RoBoTeq View Post
    I already have a piston.

    I'll need to install a txv and replace the piston with a larger sized one.

    Seeing that I still have not got around to finishing my condensate pump drain and am still using a bucket with a cut off switch, how soon do you think I will get to doing this experiment?
    LOL.

    Well, maybe by spring of 2020.
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  12. #25
    Join Date
    Mar 2007
    Location
    A Lan Far, Far Away in Podunk, Georgia
    Posts
    234
    Step 3 of the Goodman Expansion Valve Kit instructions sez....

    3. Remove the check piston and seal and discard.

    Maybe they already analyzed this issue and that's why step 3 is in the 'destructions'.

    Interesting about how would someone KNOW it wasn't removed without looking in there.
    Uh-Oh. PDQuick answered the question of how to tell with out looking.

    Question for you higher tech folks....

    Couldn't a restriction at the TXV cause the same symptoms as the flowrater piston being left in place?


    Which could lead one to suspect the piston wasn't removed?

  13. #26
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,804
    Yes it could.
    So you would have to open the fitting up to find out.
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